Various coating and printing procedures are known wherein the viscous coating medium is transferred from a container onto a roller, in which the roller is partly submerged in the viscous coating medium and also forms one wall of the container.
In order to regulate the amount of viscous coating medium, it is customary to utilize an adjustable doctor blade system against the roller surface. When using a smooth surface roller, the required film thickness is adjusted by the distance between the doctor blade and the roller surface, resulting in a regulated transfer of the coating medium thickness. But, when using an etched roller, the quantity of coating medium transferred is determined by the size and quantity of screened etchings on the roller surface. The doctor blade is brought into scraping contact with the roller surface to preserve the uniformity of coating medium as determined by the recesses formed by the etching on the roller.
The transfer of a viscous coating medium onto a medium conveyor is never complete whether a smooth or an etched roller is used. Experience has shown that a certain percentage of the viscous coating medium remains in the fine etching cells, and that after each new coating, a small build-up of the viscous coating medium results. This build-up of coating medium must be regularly cleaned out, which is a very time consuming operation.
When the coating medium is an ink used in printing operations, the transfer of the coating medium has been performed by means of inking rollers, oscillating rollers and transfer rollers and, then, finally onto a printing form or plate. The more modern viscous coating media for direct or indirect letterset and planographic printing processes are manufactured with such fine distribution and transfer properties that the use of extra distributing rollers can be eliminated, thus simplifying the inking units considerably.